Immunogenicity can be significantly improved if an antigen is co-administered with an adjuvant, commonly used as 0.001% to 50% solution in phosphate buffered saline. Adjuvants are substances that enhance the immune response to antigens, but are not necessarily immunogenic themselves. Adjuvants may act by retaining the antigen locally near the site of administration to produce a depot effect facilitating a slow, sustained release of antigen to cells of the immune system. Adjuvants can also attract cells of the immune system to an antigen depot and stimulate such cells to elicit immune responses.
Immunostimulatory agents or adjuvants have been used for many years to improve the host immune response to, for example, vaccines. Intrinsic adjuvants, such as lipopolysaccarides, normally are the components of the killed or attenuated bacteria used as vaccines. Extrinsic adjuvants are immunomodulators which are typically non-covalently linked to antigens and are formulated to enhance the host immune response.
Aluminum hydroxide and aluminum phosphate (collectively commonly referred to as alum) are routinely used as adjuvants in human and veterinary vaccines. The efficacy of alum in increasing antibody responses to diphtheria and tetanus toxoids is well established and, more recently, a HBsAg vaccine has been adjuvanted with alum.
A wide range of extrinsic adjuvants can provoke potent immune responses to antigens. These include saponins complexed to membrane protein antigens (immune stimulating complexes), pluronic polymers with mineral oil, killed mycobacteria in mineral oil, Freund's complete adjuvant, bacterial products, such as muramyl dipeptide (MDP) and lipopolysaccharide (LPS), as well as lipid A, and liposomes. To efficiently induce humoral immune response (HIR) and cell-mediated immunity (CMI), immunogens are preferably emulsified in adjuvants.
Chemically defined adjuvants, such as monophosphoryl lipid A, phospholipid conjugates have been investigated (see Goodman-Snitkoff et al., J. Immunol. 147:410-415 (1991)) as has encapsulation of the protein within a proteoliposome (see Miller et al., J. Exp. Med. 176:1739-1744 (1992)).
Synthetic polymers have also been evaluated as adjuvants. These include the homo- and copolymers of lactic and glycolic acid, which have been used to produce microspheres that encapsulate antigens (see Eldridge et al., Mol. Immunol. 28:287-294 (1993)).
Nonionic block copolymers are another synthetic adjuvant being evaluated. Adjuvant effects have also been investigated for low molecular weight copolymers in oil-based emulsions (see Hunter et al., The Theory and Practical Application of Adjuvants (Ed. Stewart-Tull, D. E. S.). John Wiley and Sons, N.Y., pp51-94 (1995)) and for high molecular weight copolymers in aqueous formulations (Todd et al., Vaccine 15:564-570 (1997)).
Desirable characteristics of ideal adjuvants include any or all (preferably most and most preferably all) of:
(1) lack of toxicity; PA1 (2) ability to stimulate a long-lasting immune response; PA1 (3) simplicity of manufacture and stability in long-term storage; PA1 (4) ability to elicit both CMI and HIR to antigens administered by various routes; PA1 (5) synergy with other adjuvants; PA1 (6) capability of selectively interacting with populations of antigen presenting cells (APC); PA1 (7) ability to specifically elicit appropriate T.sub.H 1 or T.sub.H 2 cell-specific immune responses; and PA1 (8) ability to selectively increase appropriate antibody isotype levels (for example IgA) against antigens.
At this time however, the only adjuvant widely used in humans has been alum. Other adjuvants, such as Sponin, Quil A, and the water-in-oil adjuvant, Freund's with killed tubercle bacilli (Freund's complete) or without bacilli (Freund's incomplete), have had limited use in humans due to their toxic effects; and, concerns have been raised as to undesirable effects in animals. Simply, many adjuvant formulations have been described but most are never accepted for routine vaccines, and few have been evaluated in humans, mainly due to their toxicity.
For example, the mineral oils used as adjuvants in certain animal vaccines are not readily degraded and persist at the site of injection thereby causing unacceptable granulomas; and, in general adjuvant formulations such as mineral compounds oil emulsions, liposomes and biodegradable polymer microspheres cause local reactions due to depot formation at the site of injection.
In fact, the adjuvant effect of most experimental adjuvants has been associated with the adverse effects they elicit.
For instance, adjuvants that act as immunostimulators such as muramyl dipeptide, lipopolysaccaride, lipid A, monophosphoryl lipid A, and cytokines such as IL-2 and IL-12 can also cause systemic side-effects (general toxicity, pyrogenicity), limiting their use.
Accordingly, a problem in the art is a need for adjuvants. There remains a need for improved adjuvants that are safe and economical to manufacture for human and veterinary vaccines (reviewed by Gupta and Siber, Vaccine 13:1263-1276 (1995)).
Insect cells from S. frugiperda and other Lepidopteran insect species have been described in the literature and their general use to support the infection and replication of baculoviruses and the production of recombinant proteins is well known (see, e.g., Smith et al., U.S. Pat. No. 4,745,051 (recombinant baculovirus); Richardson, C. D. (Editor), Methods in Molecular Biology 39, "Baculovirus Expression Protocols" Humana Press Inc. (1995)); Smith et al., "Production of Human Beta Interferon in Insect Cells Infected with a Baculovirus Expression Vector," Mol. Cell. Biol., 3(12):2156-2165 (1983); Pennock et al., "Strong and Regulated Expression of Escherichia coli B-Galactosidase in Infect Cells with a Baculovirus vector," Mol. Cell. Biol., 4(3):399-406. (1984); EPA 0 370 573, U.S. application Ser. No. 920,197, filed Oct. 16, 1986, EP Patent publication No. 265785).
The expression of antigens in insect cells with baculovirus expression vectors and their potential as vaccines is also well known. For example, Kamiya et al., Virus Res. 32:375-379 (1994) relates to the protective effect of glycoproteins of Newcastle disease virus expressed in insect cells following immunization with recombinant glycoproteins. Hulst et al., J. Virol. 67:5435-5442 (1993) pertains to the use of purified recombinant vaccine glycoprotein made in insect cells that protected swine from infection with the hog cholera virus.
There are vaccines where whole insect cells or insect cell membrane fractions containing a selected antigen are used. For example, McCown et al., Am. J. Trop. Med. Hyg. 42:491-499 (1990), use Spodoptera insect whole cells expressing Japanese Encephalitis Virus (JEV) glycoprotein E to immunize and protect mice against JEV. Putnak et al., Am. J. Trop. Med. Hyg. 45:159-167 (1991), use a microsomal membrane fraction of insect cells infected with a baculovirus expressing a Dengue-1 envelope glycoprotein to immunize and protect mice against challenge with Dengue-1 virus.
However, whole insect cell or insect cell membrane fraction vaccines have been a disfavored means for delivering an epitope of interest or antigen; the thinking being that isolation of the epitope of interest or antigen therefrom being necessary for the epitope of interest or antigen to be of practical utility and not just a laboratory curiosity. For instance, insect cell or insect cell membrane fraction vaccines have been used in basic laboratory tests of recombinant expression products with basic laboratory animals, but for the expression products to be considered of practical utility (e.g., useful for human medical or animal veterinary applications), it was believed that the expression products needed to be isolated further from the insect cells or insect cell membrane fractions.
Thus, heretofore there has been no recognition that insect cells or fractions thereof, e.g., Lepidopteran insect species insect cells or fractions thereof such as S. frugiperda insect cells or fractions thereof, preferably obtainable from infection with an insect virus such as a baculovirus, e.g., a recombinant insect virus such as a recombinant baculovirus, can be adjuvants, such as adjuvants for at least one epitope of interest or antigen (including allergen), e.g., an epitope of interest or antigen from expression by the recombinant baculovirus.